ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2pPA6. Reflections on the nonlinear equation of state in rock based on experiment.

James A. TenCate

EES-4 MS D443, Los Alamos Natl. Lab., Los Alamos, NM 87545

Measurements were made of the propagation of 1-D nonlinear waves (i.e., Young's mode) in a bar of Berea sandstone 3.8 cm in diameter and 1.8 m long. Both waveforms (time domain) and spectra (frequency domain) were measured. The experimental results were then compared with waveforms calculated from a numerical scheme based on the simple wave solution for 1-D waves in rock using a classical nonlinear equation of state. The numerical solution is written in MATLAB and runs quickly on a small personal computer. Attenuation was added by propagating the waveform a small distance, transforming the waveform into the frequency domain, and applying the attenuation, and then transforming back into the time domain and propagating the new waveform. The same method was applied earlier for nonlinear propagation of a sound wave in a tube of air by Pestorius and Blackstock. The experiments and simulations clearly demonstrate that a classical nonlinear equation of state is incomplete or inappropriate for describing or modeling nonlinear propagation in sandstone. Results from another model (Van Den Abeele, this session) suggest the same conclusions. [Work supported by OBES/DOE through the University of California.]